**1.** The true RL of B

The difference of level between A and B

=[(0.2955-1.155)+(2.415-0.985)] / 2

=1.435m (fall from A to B) …………………………………………………………………(1)

RL of B = 525.500-1.435= 524.065m

**2.** the combine correction for 500m curvature and refraction D = (0.0673*D*D) = (0.0673*0.5*0.5) = 0.0168m (-ve)

**3.** The collimation error

Let us assume that the line of collimation is inclined upward

Collimation error 500m is = e

When the instrument is at A

Correct staff reading at A = 1.155m

Correct staff reading at B= (2.595 – 0.0168 – e)

True difference of level between A and B
=(2.595 – 0.0168 –e ) – 1.155

=1.4232-e ………………………………………………………………………….(2)

**From (1) and (2)**

1.4232 – e = 1.4350

e= -0.0118

collimation error per 100m = -[(0.0185×100) / 500] = -0.0023m

**4.** the collimation error is assumed positive but the result is – ve. so the assumption is wrong the line of collimation is actually inclined downward.